The present invention relates generally to optical fiber handling systems, and more particularly to an optical fiber bend limiter that provides increased volume for storage of optical fiber jumper cables.
Many applications utilize an optical fiber network of interconnected optical fiber cables to enable optical communications between network locations. Optical fiber cable consists of a plurality of optical fibers surrounded by a protective sheath. Individual optical fibers consist of a small diameter core of low-loss material such as glass or plastic surrounded by a protective cladding that has a slightly lower index of refraction than the core. As is well known, fiber optic cable operates to guide transmitted light pulses with small pulse attenuation (i.e., low signal loss).
Due to the fragile nature of the fiber, there is a need to protect the fiber from external sources of stress, such as bending, pressure and strain, that can damage the fiber and/or cause degradation of the signal being transmitted via the fiber. For example, a fiber should not be bent sharply anywhere along its path. In addition to the possibility of breakage or fracture, if a fiber is bent past a critical angle, portions of transmitted light pulses will leak out, rather than being reflected within the fiber core, thereby attenuating the transmitted light pulses and degrading signal quality. Accordingly, it is necessary that a fiber be routed so that bends in the fiber be of a sufficient radius to substantially avoid occurrence of such light leakage.
The radius below which a fiber should not be bent to avoid light ray leakage is characterized as the minimum bend radius. Typically, the minimum bend radius varies with fiber design. However, in all fiber designs, bending the fiber with a radius smaller than its minimum bend radius may result in increased signal attenuation and/or a broken fiber.
Ordinarily, a unique fiber routing will be required to transmit light pulses between network locations. Over this unique route, light pulses may be propagated across several different fibers. At each transition from one fiber to another, individual fibers are connected, thereby enabling light pulses to be carried between a first fiber and a second fiber. In many cases, such as at a central office for the communications system, large numbers of fiber connections must be made and a fiber administration system is employed to manage the various connections.
In many fiber administration systems, as the optical fibers in a network enter the central office, they are directed into an optical distribution frame where the individual optical fibers are terminated in an organized manner. Such fiber administration systems are exemplified by the LGX(copyright) fiber administration system that is currently manufactured by Lucent Technologies of Murray Hill, N.J., the assignee herein.
An optical distribution frame may include one or more bays, each such bay being a vertical structure that supports a plurality of different shelves. Among the shelves in the fiber distribution frame are fiber distribution shelves. Located within the fiber distribution shelves are optical connection ports that receive the ends of all of the individual optical fibers that enter the central office for the optical fiber network. The fibers so connected at the distribution shelf ports are then interconnected as needed for a desired routing by fiber jumper cables that can be plugged into optical connectors associated with each optical connection port. In the commonly occurring case where an interconnection is required between a fiber terminated at a port on one shelf with another fiber terminated at a port for a separate shelf, the connecting jumper cable must be routed within the distribution frame between those separate shelves.
As optical fiber distribution systems evolve with growing and/or changing information-handling requirements, there is a need to install, remove, and/or reroute optical fiber jumper cables used for making connections within or among shelves in a distribution frame. However, one of the concerns in the evolution of network distribution systems is the handling and/or storage of these jumpers, and particularly the maintenance of the minimum bend radius for a jumper. A point of special concern in respect to bending of the fiber jumpers is the exit of a jumper from a shelf, typically at one side of the shelf or the other, for routing to another point in the frame. In the present art, bend limiters are attached to jumper ports at each side of a shelf. Because these current-art bend limiters are attached to the outside of the shelf, they protrude into a vertical jumper trough area at either side of the frame, thereby reducing the available space in the trough for storage and routing of jumpers. Moreover, current-art shelf bend limiter arrangements have guides that extend an excess amount below the surface of the shelf. Thus, these shelves cannot be tightly stacked in a conventional frame used in optical fiber communication systems.
Accordingly, there is a need for a new and useful storage and routing arrangement for optical fiber jumper cables that permits the easy removal, addition, and/or re-routing of optical fiber jumper cables.
In accordance with the present invention, there is provided a novel and useful cable jumper bend limiter arrangement for a fiber distribution shelf that is readily adaptable for use in conventional fiber distribution frames. The shelf jumper bend limiter arrangement of the invention operates to maintain minimum bend radii for jumpers routed via the shelf and facilitates increased storage and routing space for jumper cables routed in jumper troughs of distribution frames in which the shelves are installed.
A fiber distribution shelf is provided having at least one side arranged to be in alignment with a routing trough of the distribution frame when the shelf is installed within the distribution frame and wherein the shelf includes a first radial guide located on the shelf surface adjacent the at least one side and arranged to form a protrusion above the shelf surface, and further wherein the first radial guide is disposed substantially within the perimeter of the shelf and extends only minimally beyond the edge of the at least one side.
In a further embodiment of the invention, the fiber distribution shelf includes a first upper radial guide disposed vertically above and substantially aligned with the first radial guide. The first radial guide and the first upper radial guide cooperatively define a first jumper port for the routing of jumper cables to and from the shelf.
In a still further embodiment of the invention, the fiber distribution shelf includes at least one other side arranged to be in alignment with another routing trough of the distribution frame when the shelf is installed within the distribution frame, and wherein the shelf further includes a second radial guide located on the shelf surface adjacent the at least one other side and arranged to form a protrusion above the shelf surface, and further wherein the second radial guide is disposed substantially within the perimeter of the shelf and extends only minimally beyond the edge of the at least one other side.
In a still further embodiment of the invention, the fiber distribution shelf includes a second upper radial guide disposed vertically above and substantially aligned with the second radial guide. The second radial guide and the second upper radial guide cooperatively define a second jumper port for the routing of jumper cables to and from the shelf.
These and other aspects of the present invention will be better appreciated by reference to the following drawings and Detailed Description.